Pollutionwatch: Enjoy the sunshine – but not too strenuously

The coldest May since 1996 ended the coldest spring for over 50 years. In spite of the lower than average temperatures, last month's sunshine, when it did appear, was as strong as ever. Sunshine in May can be as strong as that in August and can be a powerful driver to create ground-level ozone, an important component of summertime smog.

Polluted continental air drifted over the UK on the 7th and 8th. Ground-level ozone reached moderate, according to the UK daily air quality index, and exceeded World Health Organisation (WHO) guidelines over much of England, Scotland and Wales. London also experienced particle pollution problems. At the end of the month, the sunny bank holiday led to moderate ground-level ozone over the southern parts of the UK on the 26th and 27th. This spread north over Scotland on the 28th and to Northern Ireland on the 29th.

Our pollution dose is a combination of the pollution in the air around us and how hard we are breathing. During summertime smog, strong sunlight and warm temperatures mean that ground-level ozone is often greatest in the afternoon and early evening. Vulnerable people are advised to avoid strenuous outdoor exercise at these times. However emerging evidence from the WHO suggests that long term, everyday exposure to ozone can affect asthma and the way that children's lungs grow. This may require a radical change in how we try to manage the health impacts of this pollutant.